When supplying a spindle of a machine tool or other such rotating part which is in a rotating state during operation with a coolant for cooling use or other fluid, a hydraulic joint is used for connecting a stationary fluid supply pipe with a channel of the rotating part. As such a hydraulic joint in a fluid supply mechanism, a rotary joint is used. In a rotary joint, a shaft which is coupled and rotates with a rotating part and a non-rotating stationary shaft which is connected to a fluid supply pipe, are arranged coaxially and made to face each other in the axial direction. The sealing surfaces of seal members attached to the respective facing end faces are made to intimately contact each other to form a face seal (seal comprised of surfaces contacting each other) to prevent leakage of fluid. Due to this configuration, it is possible to continuously supply fluid from a non-rotating fluid supply pipe to a rotating state rotating part through the rotary joint.
In a rotary joint used for a machine tool making a drawbar advance and retract etc., to make the sealing surfaces intimately contact each other, the non-rotating stationary shaft has to be made to move relative to the shaft in the axial direction. The relative movement in the axial direction, in the prior art, was performed by making the fluid power of the fluid supplied act on the upstream side end part of the supplied fluid at the stationary shaft and making the stationary shaft slide in a fitting hole (for example, see PLTs 1 and 2). The “stationary shaft” here indicates the shaft at the stationary side connected to a stationary fluid supply pipe. The case of a shaft which slides in a fitting hole without rotating is also included in a “stationary shaft”. The “upstream side” and the “downstream side” indicate the upstream side and downstream side of the supplied fluid.
In the prior art shown in PLT 1, the fluid power of the fluid supplied is made to act on the upstream side end part of the stationary shaft and make the stationary shaft slide in the fitting hole to thereby form the face seal. Further, in the prior art shown in PLT 2, in the same way as PLT 1, the fluid power is made to act on the upstream side end part of the stationary shaft. In addition, the fluid power is also made to act on a movement member slidably fit in a fitting hole and the movement member is made to abut against the upstream side end part of the stationary shaft at the start of operation so as to supplement the drive force. Note that, as one example of a machine tool making a drawbar advance and retract, one such as disclosed in PLT 3 may be mentioned.